Studies of 9 spontaneous tumors of the C3Hf/Sed mouse have been partially completed. These have shown that using 3rd generation isotransplants there is only a weak or no immunogenicity, that C parvum effect was modest in several of the tumors, that 8 of 9 tumors were highly radiation resistant, viz. TCD50 values is greater than 6000 rad. Studies of macrophage content correlated weakly with metastatic activity. These various assays should be completed during the coming year. Comparison of the efficacy of O2 30psi with Misonidazole (0.3mg/g BW i p 45 min before each irradiation) in the radiation treatment (10 equal fractions, 1 day between fractions) of 8mm MDAH-MCaIV (mammary carcinoma) demonstrated a greater efficacy of O2 30 psi. Pentobarbital anesthesia was shown to increase significantly the efficacy of O2 30psi to reduce TCD50 for fractionated irradiation of MCa. Work in hyperthermia demonstrated the thermal OER to be essentially 1.0 and for this to be independent of pH. TCD50 (Heat) of FSaII (spontaneous fibrosarcoma) growing in the foot pad decreases with tumor size.